The present invention relates generally to shielding arrangements for shielding against electromagnetic and radio frequency interference in electronic equipment and pertains, more specifically, to improvements in the construction of shielding gaskets utilized in such equipment.
A wide variety of shielding gaskets currently is available for use in connection with electronic equipment such as computers, wireless telephones and various other information and communication apparatus. Many of these shielding devices are constructed of relatively thin flexible sheets of metal and utilize spring contactors for making electrical contact at multiple locations to effect ground connections in various shielding arrangements. These spring contactors usually are in the form of cantilever spring tabs or fingers biased into contact with surrounding structures by simple bending. Appropriate contact forces generally are attained either by selecting the length of the cantilever arm, or by modifying the cross-sectional configuration of the arm to provide bending characteristics which will attain the desired contact forces. For example, deflection forces are reduced, while effective contact pressure is maintained, by increasing the length of a cantilever contactor arm. However, increased contactor arm length tends to increase stresses at the base of the contactor arm, leading to early mechanical failure and loss of electrical integrity. Modification of the cross-sectional configuration of a contactor arm often leads to a weaker, generally more flimsy gasket construction, and usually one which is more difficult to manufacture, and therefore more expensive. Moreover, the deflection of cantilever contactor arms results in increased contact area, thereby departing further from a more desirable limited point or edge contact and decreasing shielding effectiveness.
Shielding gaskets also have been constructed of elastomeric materials, usually using foamed structures rendered conductive by the incorporation of metal fibers either woven into or around the elastomeric material. The forces required to compress such a shielding gasket usually are much greater than those required for a comparable thin metal gasket because the load is distributed over a much greater area than the point or edge contacts encountered at the spring fingers of a thin metal gasket. Moreover, elastomeric gaskets are prone to oxidation and thermal degradation, both of which will lead to loss of resiliency and concomitant loss of shielding effectiveness.